1. Field of the Invention
The present invention relates to a probe device with a bending actuator in which a distal end portion is formed of an axially expanding and contracting shape memory alloy.
2. Description of the Related Art
Generally, endoscopes and other like devices having probes such as insert tubes (or insert portions), which can be inserted to the subject's interior for the purpose of inspecting the interior of subjects such as chemical plants and living bodies, are widely used for non-destructively inspecting the subject's interior.
Ducts, tracts or cavities leading to the subject's interior are sharply curved in general in many cases. Accordingly, when a location to be inspected is at a deep position, it is difficult to introduce the distal end side of a probe up to such a location. This results in that the inspection takes plenty of time and, if the subject is a living body, the living body is subjected to substantial discomfort.
In the related art, there have been disclosed several examples of a device having a bending actuator, i.e., a bending drive mechanism, in which the distal end side of a probe is formed into a bendable portion capable of being driven to bend as desired when the probe is operated from the side near an operator (i.e., the proximal end side), thereby facilitating introduction of the probe into the subject's interior.
For example, U.S. Pat. No. 4,794,912 discloses a borescope or endoscope provided with a fluid dynamic muscle. This prior art is designed to produce a drive force in the axial direction by a bag of which volume can be diminished using a fluid. However, producing the axial drive force requires a reduction in the dimensions of the bag not only in the axial direction but also in a direction perpendicular to the axial direction. Accordingly, when this prior art is used with probes in those applications where the probes are desired to be small and thin in diameter in order so that the probes can be inserted to even thin ducts or tracts, or the friction generated upon insertion of the probes can be reduced (particularly, to make a living body feel less pain), there occurs a disadvantage of rendering outer diameters of the probes too large.
Further, U.S. Pat. No. 4,794,912 discloses an endoscope having a bendable portion formed of a shape memory alloy which is driven to bend as desired. With this prior art, because the shape memory alloy is used in the form of a single cable, it is required to increase a diameter of the cable for providing a drive force necessary. In this case, a reduction in flexibility of the probe portion including the shape memory alloy built therein adds the friction resistance produced upon the probe portion being inserted to sharply curved ducts or tracts, and thus makes the inserting operation difficult.
Meanwhile, Japanese Patent Laid-Open No. 61-197,770 discloses a shape deformable member in which at least two shape memory alloys having different temperatures of transformation are combined with each other in such twisted fashion as being capable of deforming into three or more shapes. In this prior art, a linear shape deformable member shown in FIG. 2(a) of the drawings in the cited Japanese Patent Laid-Open can be deformed by heating into a coiled shape with a large spiral pitch as shown in FIG. 2(c) and a coiled shape with a small spiral pitch as shown in FIG. 2(c). Also, another shape deformable member formed by bonding two plate-like shape memory alloys having different temperatures of transformation together (see FIG. 6(a) in the cited Japanese Patent Laid-Open) can be deformed by heating to bend from a linear shape through different amounts in a direction vertical to the plate surface (see FIGS. 6(b) and 6(c)).
The last mentioned prior art teaches that use of shape memory alloys having different temperatures of transformation enables the shape deformable member to deform into three or more shapes which cannot be realized in the case of using shape memory alloys having the same temperature of transformation. Therefore, when that prior art is employed for deformation into a number of shapes, it is necessary to use a number of shape memory alloys having different temperatures of transformation. This means that in the application field of inserting tubes which need to be set to any desired bending amounts, use of a large number of shape memory alloys is necessary in order to change the axial length of the shape deformable member in a substantially continuous manner.
Since drive forces required for the bendable portions of probes to bend as desired are generally different dependent on probe diameters, kinds of members built in insert tubes, and so forth, the cross-sectional area of the shape deformable member must be varied to set an appropriate drive force for each of the probes. Application of the last mentioned prior art to such a case results in the disadvantage of requiring the preparation of quite a large number of shape memory alloys with several different diameters for each alloy, as components used for construction of the shape deformable member, and also an arrangement of those shape memory alloys so that the total cross-sectional area becomes equal to a cross-sectional area determined from the viewpoint of producing a necessary drive force, which remarkably pushes up the cost when the above prior art is used with a bending drive member.